descension

noun2

1. •
   (no longer used) Descent; the act of descending.

   • Death is followed by either ascension into a higher plane or descension into a lower plane.
2. •
   (no longer used) The descent below the horizon of a celestial body.

   • For in regard of time (as we elsewhere declare) the stars do vary their longitudes, and consequently the times of their ascension and descension. — 1646